Century 41 Operating instructions

CENTURY 41

AUTOPILOT

&

CENTURY 41

FLIGHT DIRECTOR/AUTOPILOT

PILOT’S OPERATING HANDBOOK

JANUARY 1985

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TABLE OF CONTENTS

REVISION LOG

FORWARD................................................................................. 4

FEATURES................................................................................ 6

Roll Axis and Pitch Axis .......................................................... 7

C41 Operating Controls........................................................... 8

Master Disconnect/Trim Interrupt........................................... 10

Lateral Operating Modes ......................................................... 12

Pitch Operating Modes ............................................................ 15

Review of Interlocks and Failure Warnings. .......................... 18

Electronic Rudder Trim (Optional).......................................... 19

Yaw Damper System (Optional) .............................................. 20

Directional Gyro........................................................................ 21

C41 Flight Director Steering Horizon...................................... 24

C41 Flight Director Steering Horizon Two Cue (Optional).... 26

C41 Flight Director Steering Horizon Two Cue(4”)(Optional) 27

NSD-360A and Other Compass Systems ............................... 30

C41 Operating Techniques...................................................... 34

Localizer (LOC) Approach....................................................... 35

Glideslope (GS) Automatic Arm and Couple ......................... 41

Localizer Back Course (LOC BC)............................................ 43

VOR Approach.......................................................................... 47

VOR Navigation ........................................................................ 53

Maintenance.............................................................................. 57

Emergency Operation .............................................................. 58

Product Improvements............................................................. 59

Limited Warranty Century Flight Systems Autopilot............. 60

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LOG OF REVISIONS

JANUARY 1985---ORIGINAL

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FOREWORD

The Century Flight Systems Century 41 Autopilot is an advances General

Aviation Flight control System utilizing “State of the Art” electronic techniques.

In this handbook we have detailed the features, functions, and general operating

instructions of the Century 41 System.

May we suggest that you do two things:

1. Read this handbook and your Airplane Flight Manual Supplement. This

handbook presents general operating procedures. Each aircraft installation

has an Airplane Flight Manual Supplement or Autopilot Handbook that

contains FAA approved flight procedures and operation limitations in that

particular model aircraft. The appropriate AFM Supplement is a document

which must be aboard U. S. Registered Aircraft with the autopilot installed.

2. Spend some VFR time with the equipment to become familiar with its

operation so that you may have the full benefit of its capabilities.

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THE CENTURY 41 FLIGHT DIRECTOR/AUTOPILOT

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FEATURES

The Century 41 Autopilot

This Autopilot only version uses a standard artificial horizon in combination with

a directional gyro (DG) or an NSD-360A Horizontal Situation Indicator (HSI). It

may optionally use other compatible heading systems.

The Century 41 Flight Director/Autopilot

When computed steering information is displayed on the horizon the system

becomes a Flight Director. The three steering horizons presently used in the

Century 41, are as follows:

1. 3-inch Single Cue (52C77).

2. 3-inch Two Cue (52D177).

3. 4-inch Two Cue (Cross Pointer) with raw data Glideslope and Localizer

(52D178).

Both versions of the Century 41 are basically the same and the autopilot only

version can be converted to a Flight Director by the addition of one of the above

steering horizons. Either version may incorporate an optional Century Yaw

Damper.

An outstanding feature of the Century 41 is that it has a rate based inner loop for

short term dynamics. This means that rate information is derived from the

horizon so that motion about the roll and pitch axis is programmed to occur at a

rate approximate to the activity. Examples of controlled rate motion are as

follows:

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ROLL AXIS:

Heading Command - Roll at 5° per second diminishing near bank limit.

Navigation Soft Mode - Roll at 2.5° per second to reduce bank limit (8°).

Gust Disturbances - Resisted by instantaneous servo command.

PITCH AXIS

Command Attitude - 0.7° per second attitude change.

Command Altitude Change - 0.7° per second attitude change until reaching 500

feet per minute climb or descent.

Gust Recovery - Maximum rate consistent with passenger comfort.

Maximum System Capability - 2.4 ° per second.

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CENTURY 41 OPERATING CONTROLS

The Mode Programmer push button switch placards are lighted and dimming is

provided by the control panel light dimmer switch.

The Mode Annunciator light intensity is a controlled automatically by a self-

contained ambient light level sensor; this feature provides optimum Mode

Annunciator light level for all cockpit lighting conditions. The Century 41

Autopilot is activated with the Aircraft Master switch and operates in a low power

state until the Flight Director display and/or autopilot operation is desired. Mode

selection is made by pushing the desired mode switch on the Mode Programmer.

The selected mode will be illuminated on the Mode Annunciator.

A separate Trim Master switch is located on the Control Panel.

Auto Trim Function is activated by the Autopilot Engage switch.

A Go-Around switch is located on the left horn of the pilot’s control

wheel or on the left throttle arm.

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AUTOPILOT ON - OFF - Autopilot engage is

accomplished by pressing the momentary ON-OFF

rocker switch on the left side of the Programmer.

When operating as an autopilot only version or as a

Flight Director with the steering bars stowed., the

Autopilot will engage in the HDG and ATT modes with

synchronization to the existing aircraft pitch attitude.

In the Flight Director version (steering bars in view),

the Autopilot will engage in the previously

programmed lateral and pitch modes.

The HDG mode the aircraft will track the heading

selected on the DG or HSI. In NAV, APR or REV

modes the aircraft will intercept and track any

properly programmed radio-defined course.

Instructions for proper radio set up in these modes

are included in this manual.

In ATT mode the autopilot will synchronize to the

aircraft pitch attitude upon engagement.

In ALT mode the aircraft will synchronize to the pressure altitude present at the

time of engagement.

The autopilot may be disengaged by pressing the momentary ON-OFF rocker

switch on the programmer; by pressing the AP DISC. Switch on the control

wheel trim switch; by pressing the master disconnect switch, if present, on the

control wheel; or by interrupting power at the Aircraft Master switch.

Disengagement causes the AP annunciator to flash for 5 seconds.

MANUAL ELECTRIC TRIM - With the Aircraft and Trim Master switches on, a

manually operated electric trim function is activated by the control wheel trim

switch. This switch serves a dual function:

1. Disengage the autopilot.

2. Activate manual electric trim.

Pressing down on the center rocker bar causes autopilot disengagement. This

action also activates trim enabling power. Movement of the bar forward and aft

causes the trim to run in a corresponding down-up direction.

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MASTER DISCONNECT TRIM INTERRUPT

Many Century 41 autopilots incorporate an additional switch on the control wheel

(usually a red button). Pressing this button will disconnect the Century 41, the

Yaw Damper, (if installed), and will interrupt the operation of the Trim System.

Release of the button will restore power to the Trim System but AFCS re-

engagement is necessary to resume automatic flight.

AUTO TRIM - The Century 41 Autopilot is equipped with automatic pitch trim.

When the Trim Master switch is on, Auto Trim is activated by engaging the

autopilot. If all is normal no indication of Auto Trim will occur on the Mode

Annunciator. Should the Trim Master switch be turned off or if trim power failure

should occur while the autopilot is engaged, AUTO TRIM will flash on the Mode

Annunciator.

The Auto Trim is fail safe in design. Should a trim malfunction occur (other than

power failure), FAIL and AUTO TRIM will flash on the Mode Annunciator and the

trim servo will disengage.

PREFLIGHT AUTOMATIC TEST SEQUENCE

+

The Century 41 is equipped with a comprehensive automated self-test program

which, when activated on the ground prior to autopilot engagement will test the

following:

1. Validity of gyro excitation monitor.

2. Automatic trim failure monitor circuits.

3. All Mode Annunciator indicators.

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COMMAND TRIM - To be performed before first flight of each day.

PROCEDURE:

1. Set Trim Master switch to ON.

2. Using the control wheel trim switch, verify normal trim system up and down

operation.

3. Depress and hold center rocker bar on control wheel trim switch. Observe

that trim system does not operate.

4. Release center rocker bar and move the rocker bar forward and aft. Observe

that trim system does not operate with any single action.

CAUTION

Any failure of the above procedure indicates that a failure exists in the system

and the Command Trim shall not be operated until the failure has been identified

and corrected.

AUTOPILOT/AUTO TRIM - To be performed before first flight each day.

PROCEDURE:

1. Verify Trim Master Switch is ON and that the autopilot is disengaged.

2. Press and hold TEST push button switch on Mode Annunciator. Verify the

following sequence, (each indication will last approximately two seconds).

a. All annunciators illuminate with FAIL and AP flashing.

b. AUTO TRIM flashes, goes steady then flashes.

c. All annunciators illuminate steady.

d. After three to five seconds, AUTO TRIM and FAIL will flash for third time.

3. With TEST push button switch still depressed, use the control wheel trim

switch to verify trim system will not operate in either up or down direction.

4. Release the TEST push button switch. All annunciators except HDG and ATT

extinguish.

CAUTION

Any deviation of the above sequence indicates a failure exists in either the

primary system or in the monitor circuits and trim system shall not be operated

until the failure has been identified and corrected.

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LATERAL OPERATING MODES

HEADING - In HDG mode the autopilot will capture and hold the heading

selected on the DG or HIS. HDG annunciator will illuminate.

NAVIGATION - In NAV mode the autopilot has an automatic 45° VOR-LOC

intercept angle and selected angle intercepts when equipped

with the NSD-360A or other HIS. NAV annunciator will illuminate.

When executing an intercept, the rate at which the aircraft is closing upon the

selected radio-defined course is determined by the computer and at the proper

time an on-course turn is initiated. After course interception, “window logic”

circuits observe that the course error is within ± 11° and the radio deviation is

less than ± 10% of full scale. This logic initiates crosswind correction, radio gain

reduction, lowers the roll rate to 2.5° per second and limits bank angles to 8° to

produce an automatic “soft” navigation mode when tracking VOR. The system

will remain in soft mode during station passage. However, if a new course which

requires re-intercept is selected, the soft mode will unlock and the intercept

sequence will reoccur.

NOTES

The NAV mode should be used when executing a holding pattern on the

localizer to prevent automatic glideslope coupling.

When radio receiver is tuned to a localizer frequency, the GS coupler will

operate with localizer (APR) dynamics in the NAV mode.

HEADING SYSTEMS

In systems equipped with DG the autopilot heading bug must be set to match the

selected VOR radial.

In systems equipped with an NSD-360A or other HIS instrument, the heading

bug is disabled when the NAV, APR or REV modes. In these modes the azimuth

information to the autopilot is provided by the radio course pointer.

HDG

NAV

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NOTES

In systems equipped with an NSD-360A or other HSI always set the radio course

pointer to the Front Course Inbound Heading when operating in the APR or REV

modes.

In systems equipped with a DG, always set the heading bug to the final

approach heading to the airport.

See section on operating techniques for additional operating instructions for the

NSD-360A.

SELECTED INTERCEPT ANGLE

In systems equipped with an NSD-360A or other HSI, a selected intercept angle

function is available while operating in the NAV, APR and REV modes.

Selected intercept is initiated by performing the following steps:

1. While operating in the HDG mode, set the course pointer to the

desired radial.

2. Set the heading bug on the NSD to the desired intercept

heading.

3. Press the HDG and NAV, HDG, and APR or HDG and REV

mode buttons simultaneously.

HDG NAV

OR

HDG REV

HDG APR

OR

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Both HDG and the selected lateral mode will now illuminate on the annunciator.

As the aircraft begins its on course turn, the HDG annunciator will extinguish

indicating that the system has captured the radio signal and is now receiving

azimuth input from the course pointer.

NOTE

If valid radio signal is lost after initiating a selected angle intercept, the

applicable navigation mode annunciator will flash the autopilot will remain in the

HDG mode.

APPROACH - The APR mode provides automatic 45° VOR-LOC intercept angle

and selected angle intercepts when the system is equipped with an

NSD-360A or other HSI. The intercept, crosswind and tracking

sequences are similar to those described in the NAV mode of

operation except that softening is delayed for 90 seconds after

intercept and bank angle limits are reduced to 12° at 3.6° per

second maximum roll rate. The APR mode has additional enabling

logic for the automatic glideslope arm, capture and track sequence

and must be used on ILS approaches.

APR

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REVERSE (Back Course) - The REV mode is for use in tracking

the localizer back course inbound and front course Outboard.

45° automatic intercepts, selected angle intercepts, crosswind correction and

tracking are as described in the APR mode except that response to radio signals

are reversed.

NOTES

When using an NSD-360A or other HSI, always set the course pointer to the

inbound front course localizer heading.

When using a DG, always set the heading bug to the final approach heading to

the airport.

PITCH OPERATING MODES

ALTITUDE - ALT mode will cause the aircraft to maintain the

pressure altitude present at the time of ALT engagement or at the

time of autopilot engagement if ALT has already been selected.

ALT may be engaged at maximum rate of climb or descent, but for passenger

comfort, rate of climb or descent should be reduced to 1,000 feet per minute

prior to ALT engagement. Corrections. To ALT may be made as described in

paragraph on the Pitch Data Modifier.

REV

ALT

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ATTITUDE - ATT mode places pitch command with the pitch data

modifier. Pitch is always synchronized to the existing aircraft

attitude. When engaging the autopilot in ATT mode or when

transferring the system to ATT from ALT or Go-Around modes the

aircraft will maintain its existing attitude.

PITCH DATA MODIFIER - The pitch data modifier is a momentary

type switch, located on the right side of the Mode Programmer,

used to modify either the selected altitude or attitude.

When the autopilot is engaged in ATT mode, holding the pitch data

modifier either up or down will cause the aircraft to rotate at 0.7°

per second until a vertical speed of 500 feet per minute is reached.

Upon release of the modifier, the system will synchronize to the

attitude present at the moment of release.

When the autopilot is engaged in ALT mode, holding the Pitch Data Modifier

either up or down will cause the aircraft attitude to change at 0.7° per second

until a vertical speed of 500 feet per minute is reached. Upon release of the

modifier, the system will synchronize to the altitude present at the moment of

release.

GLIDESLOPE COUPLING - In the presence of selected APR mode only and

other enabling logic, the glideslope function is fully automatic. Therefore, no GS

engage switch is used. Glideslope may be entered from either ATT or ALT

mode, from either above or below the glideslope.

Capture of the glideslope depends upon satisfying conditions which will

complete the arming sequence. After arming, capture will occur just before

glideslope interception so as to rotate smoothly to interception. This

“anticipative capture” point is determined by the rate of closure satisfying a

computer equation. In order for the glideslope to arm, the following conditions

must exist simultaneously:

1. No 1 NAV radio channeled to a localizer frequency.

2. Localizer deviation must be less than 80% of full scale.

3. A valid localizer signal (no flag).

4. A valid glideslope signal (no flag).

5. APR mode selected.

When these conditions are met the GS Annunciator will illuminate in conjunction

with the active pitch mode light indicating glideslope is armed. When

“anticipative capturing” occurs, the active pitch mode light will go out leaving

only the illuminated GS annunciator to indicate that transition to the glideslope

signal has occurred. The GS mode may be deactivated by selection of any

other pitch mode (ALT, ATT, GA) but automatic recapture of the glideslope may

occur in ALT or ATT modes.

ATT

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NOTES

The NAV mode should be used when executing a holding pattern on the

localizer to prevent automatic glideslope coupling.

When radio receiver is tuned to a localizer frequency, the GS coupler will

operate with localizer (APR) dynamics in the NAV mode.

GO-AROUND - A separate go-around mode switch is located on

the throttle or control wheel. Activation of this mode results in a

pitch up attitude to best single engine rate of climb. With two

engines operating it will result in an approximate cruise climb.

Activation of the GA mode does not alter the lateral mode.

CWS MODE - The system is equipped with pitch sync

switch located on the left horn of the pilot’s control

wheel. When depressed this switch will disengage

the roll and pitch servos to allow manual

maneuvering.

When released the system will re-engage in the

lateral (roll) mode previously in use.

If the pitch is in ALT mode the system will

synchronize to the pressure altitude present upon

release of the CWS switch.

If the pitch axis is in ATT mode the system will

synchronize to the attitude present at the time of

release.

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REVIEW OF INTERLOCKS AND FAILURE WARNINGS

The Century 41 System includes a number of automatic interlocks that will

prevent system operation or individual mode operation if the input information is

not valid or if other prerequisite conditions do not exist. In addition to the

interlocks, the system will annunciate various failure conditions as advisory

information for the pilot. Following is a brief description of interlocks and

warnings provided.

INTERLOCKS

Autopilot engagement is inhibited unless valid gyro excitation is being provided

by the system.

Selection of ALT mode is inhibited if the system altitude information is unreliable

or if the entire system has not been powered for a time sufficient to allow

temperature stabilization, usually 2 to 6 minutes depending on ambient

temperature.

If the navigation information becomes invalid during selected angle intercepts

the appropriate NAV/APR/REV annunciator will flash and automatic mode

switching from HDG to the armed navigation mode will be inhibited.

WARNINGS

LOW VOLTAGE - When the aircraft bus voltage provided the system falls below

the minimum required for reliable system function, any mode annunciator not

already illuminated will flash.

ATTITUDE GYRO EXCITATION - Absence of valid gyro excitation will cause the

autopilot to disengage and the AP and FAIL annunciators to flash. The autopilot

cannot be re-engaged until this condition is corrected.

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AP DISENGAGEMENT - Anytime the autopilot is disengaged the AP

annunciator will flash for approximately 5.0 seconds, then remain off.

NAVIGATION INFORMATION INVALID - The appropriate navigation mode

annunciator will flash when selected and invalid navigation signals are present

(NAV Flag in view).

GLIDESLOPE INFORMATION INVALID - The GS annunciator will flash when

glideslope information is invalid or any other GS Arming condition is lost (GS

flag in view) after glideslope capture. If valid glideslope information or any other

GS Arming condition is not available during the arming sequence, the system

will not arm and glideslope capture will not occur.

AUTO TRIM FAILURE - When the autopilot is engaged and the auto trim

malfunction monitor detects a trim failure, the trim servo engage solenoid is

deactivated and the AUTO TRIM and FAIL annunciators will flash.

When the autopilot is engaged and trim system power is available, the Auto Trim

is normally on without annunciation. If trim power is lost during autopilot

operation the AUTO TRIM annunciator will flash.

ELECTRONIC RUDDER TRIM

(Optional)

An optional automatic Rudder Trim System is available for some aircraft models

for use with the Yaw Damper System. The function of the Rudder Trim System

is to adjust the rudder trim tab to relieve rudder forces. The System is

interlocked with the main Autopilot and the Yaw Damper so that both must be on

for the rudder trim to be operational.

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YAW DAMPER SYSTEM

(Optional)

The Century Flight Systems Yaw Damper System is a frequently

installed option with the Century 41. The system has only one

control - the ON-OFF Push Button. The system is an independent

subsystem that may be used with or without the Century 41.

For pilot assistance and passenger comfort, its function is to add addition

stability to the yaw axis of the aircraft and minimize any tendency to hunt or

dutch roll in the aircraft. In addition, the Yaw Damper incorporates an “electronic

ball” to assist in coordinating turns and trimming the aircraft under conditions of

asymmetric power. The Yaw Damper does not ordinarily compensate for rudder

trim variations with speed changes and therefore may “bump” the rudder controls

slightly when engaged or disengaged at speeds other than that for which it is

adjusted.

The Yaw Damper is engaged by pressing the ON-OFF Push Button. It is

disengaged by pressing the ON-OFF Push Button or by pressing the Master

Autopilot Disconnect-Trim Interrupt Button.

The Yaw Damper switch is a lighted annunciator type switch which is connected

to the panel lamp rheostat controlling the light intensity in the area of installation.

On some installations, the light intensity for day operations is low under some

ambient light conditions. For this reason, the knob edge is engraved with a

black index line that is in view when the system is “OFF” and hidden when the

system is “ON”.

PUSH-ON

Y/D

PUSH-OFF

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Century 41 Operating instructions

Century 41 Operating instructions

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